Lead-free impression material



LEAD-FREE IMPRESSION MATERIAL Wallace A. Erickson, Hartley C. Ericson, and Vytautas Grakauskas, Chicago, 111., assignors to Wallace A. Erickson & Co., a corporation of Illinois No Drawing. Application November 12, 1953 Serial No. 391,732

7 7 Claims. (Cl. 106-3835) This invention relates to an impression material whicn contains as one of its ingredients a non-reversible hydrocolloid which is capable of forming an elastic gel. This impression material has as one of its advantages, the property of forming a satisfactory elastic gel without necessitating the inclusion of lead or lead-containing material.

The alginate-type impression materials have come into great favor in the last decade, but one problem which they present is that of forming a good plaster surface of suflicient hardness and smoothness.

In the early alginate-type impression materials, it was necessary to apply a fixative to the surface of the material in order to procure the proper surface. Later, it was suggested that an alkali metal silico fluoride could be embodied in the material for the same purpose. This material, however, produces a lowering of viscosity in the material and also produces too great rigidity after standing for more than a short time.

Furthermore, in order to get best results from alkali metal silico fluorides or from other fluorides such as alkali metal titanium fluorides, it has been customary to employ a lead salt such as lead silicate.

While there has been no indication of any general toxicity in lead silicates as properly prepared and used, there is a general desire to avoid the presence of lead in a material which has to be placed within the mouth. If any of the lead-containing material is swallowed, however, lead ions are produced in the stomach.

We have discovered that the difliculties aforesaid, as Well as the presence of lead, can be avoided where a titanium fluoride is employed, where an alkali metal titanium fluoride is employed, or where magnesium titanium fluoride is employed and this is particularly true if a small amount of zinc oxide is introduced into the impression material. The compounds so produced not only have a surface of the desired characteristics when set, but do not produce excessive flow of the impression material in the mixing stages and the impression material does not become unduly rigid on ordinary standing. It

remains elastic for at least 60 hours, so that it may i be removed from a plaster model without damage to the model even after standing several hours.

The preferred alginates are the sodium and potassium alginates, although other alkali metal alginates may be employed. Carboxy methyl cellulose or its soluble salts and gelable derivatives may be employed. The alkali metal pectin compounds or pectates may likewise be employed.

Alginate-type materials are normally reacted with a metallic salt which is usually a form of calcium sulfate, either the dihydrate or the hemi-hydrate. All of these salts are relatively slowly-soluble materials. Some lead salts have likewise been suggested in place of the calcium.

It is customary in gel-forming impression materials of this type to employ a retarder. These are normally alkali metal carbonates, oxalates, or phosphates. It is preferred to employ molecularly dehydrated phosphates 7, 2,824,811 Patented Feb. 25, 1958 2 such as tripolyphosphate or pyrophosphate. Metaphosphates, however, are likewise suitable. Trisodiumphosphate may be used, but is far less adaptable and more critical in its proportions.

An inert filler is likewise employed. This may be powdered talc, clay, calcium carbonate, silica, or diatomaceous earth. Some organic fillers may likewise be used, such as starch, waxes, or the like. The preferred filler is a diatomaceous earth.

The presence of the zinc oxide in its usual very finely divided form adds strength and produces a better plaster surface. The mechanism of the zinc oxide reaction is not thoroughly understood, but it is believed to supply zinc ions when, and only when, the impression material during the course of setting becomes acid, and at this stage these ions react with free alginate.

The preferred impression material has the following composition:

Percent by weight Calcium sulfate dihydrate 15 The titanium fluoride as used in the above formula is for the purposes of this application, only, intended to cover TiF MgTiF and the alkali metal titanium fluorides.

It should be realized, of course, that the chemicals will vary in their particle size and the presence of impurities may markedly affect the composition. This is particularly true of the alginates which also vary markedly in viscosity. The proportions of retarder, alginate and fluoride may be varied according to differences in the natural characteristics of the ingredients to control setting time and other characteristics in accordance with well recognized skills of the art.

Within limitations of desired end use, the following range of ingredients may be employed for impression materials:

540% 1-15 l-l5% 530% 1-15 10-80% Pigment Flavor calcium sulfate dihydrate zinc oxide poly-, pyro-, and/ or metaphosphates alkali-metal alginate titanium fluoride inert filler One additional advantage of the present material which has not been available in other alginate-type impression materials is that it may be used for duplicating material in conjunction with casting investments, since it can still be peeled away after lapse of a substantial period of time.

An additional advantage is that the material is free from lead.

The foregoing detailed description has been given for clearness of understanding only and no unnecessary limitations should be undesrstood therefrom as modifications will be obvious to those skilled in the art.

We claim:

1. A substantially lead-free dental impression material consisting essentially of a non-reversible hydrocolloid, a water-soluble calcium compound which provides calcium ions in solution which are chemically reactive in solution with said hydrocolloid, said calcium compound being present in said material in an amount suflicient to form an elastic gel by reacting with said hydrocolloid in solution, one to fifteen percent by Weight of zinc oxide which serves as a hardening agent in an acid solution,

zinc oxide. 6 v

2. 'An impression material as set forth in claim 1 1 wherein the hydrocolloid ,is a water-soluble -alginate.'

3. An impression material as set forth in claim 1 wherein the fluoride is TiF 4. An impression mater al as set forth in claim 1 V wherein the fluoride is MgTiF- g 5,;An impression material as-set forth in claim 1 V wherein the fluoride is Me TiF wherein Me .is an alkali 6, A lead-free dental impression material'consis'ting essentially of a non-reversible hydrocolloid, calcium sulfate which provides calcium ions in solution Which'are chemically reactive in solution with said thydrocolloid, said calcium compound being present in said material in an amount suificient to form an elastic gel by reacting,

with said hydrocolloid in solution, one to fifteen percent by weight of zinc oxide which serves as a hardening agent 7 7 in an acid solution, and one to fifteen percent by weight of a fluoride from the group consisting of TiF MgTiE and Me TiF ,.wherein Me is an alkali metal, which pro-- vides fluoride ions when said material is in solution and, at the same time, provides an acidic medium which solubilizes the'zinc oxide.

7. An impression materialtas set forth in claim 6 wherein the hydrocolloid is :1 wat r-Somme alginate;

References Cited in the file of this patent UNITED STATES PATENTS 1,194,176 Heal ly 1 1 Aug. 8, 1916 2,390,137 Vallandigham De.,4, 1945 1 1 2,424,895 Noyes July, 29, 1941 2 ,623,808 Meyer Dec. 30, 1952 2,628,153 Noyes Feb. 10,1953 2,652,312 1 Pink -1 Sept, 15, 1953 FOREIGNPATENTS V a 691,423 Great Britain May 13; 1953 

1. A SUBSTANTUALLY LEAD-FREE DENTAL IMPRESSION MATERIAL CONSISTING ESSENTIALLY OF A NON-REVERSIBLE HYDROCOLLOID A WATER-SOLUBLE CALCIUM COMPOUND WHICH PROVIDED CALCIUM IONS IN SOLUTION WHICH ARE CHEMICALLY REACTIVE IN SOLUTION WITH SAID HYDROCOLLOID, SAID CALCIUM COMPOUND BEING PRESENT IN SAID MATERIAL IN AN AMOUNT SUFFICIENT TO FORM AN ELASTIC GEL BY REACTING WITH SAID HYDROCOLLOID IN SOLUTION, ONE TO FIFTEEN PERCENT BY WEIGHT OF ZINC OXIDE WHICH SERVES AS A HARDENING AGENT IN AN ACID SOLUTION, AND ONE TO FIFTEEN PERCENT BY WEIGHT OF FLUORIDE FROM THE GROUP CONSISTING OF TIF4, MGTIF6 AND ME2TIF6, WHEREIN ME IS AN ALKALI METAL, WHICH PROVIDES FLUORIDE IONS WHEN SAID MATERIAL IS IN A SOLUTION AND, AT THE SAME TIME, PROVIDES AN ACIDIC MEDIUM WHICH SOLUBILIZES THE ZINC OXIDE. 